Power electronics (PE) take a critical role in electricity transformation, transmission and application in modern industrial utilization. Improving the efficiency while maintaining the stability of performance of electrical system and device is a continuously studied topic. In high power PE applications, hundreds and thousands of watts of heat is generated in conduction and switching status, as a result of that, design of cooling system is essential in a PE system design process. This thesis proposed a real-time Thermal Hardware-In-the-Loop (THIL) simulation methodology to evaluate performance of cooling system of power semiconductors in a power circuit. This method required less energy and cost rather than traditional completely physical test as well as providing credible result of semiconductor junction temperature and instantaneous power dissipation.